1. Field of the Invention
An apparatus and a method consistent with the present general inventive concept relate to an image forming apparatus and a control method thereof, and more particularly, to an image forming apparatus and a control method thereof having a light exposing unit to precisely expose an image carrying body.
2. Description of the Related Art
An electrophotographic image forming apparatus prints an image on a printing medium through a series of processes of charging, exposing, developing, transferring, fusing and cleaning. Examples of an electrophotographic image forming apparatus include a laser printer, an electronic copier, a multifunction device, etc.
The electrophotographic image forming apparatus includes a photosensitive body, and a light exposing unit exposing light upon a surface of the photosensitive body in a main scanning direction to correspond to an image to be printed. If the surface of the photosensitive body is exposed to the light from the light exposing unit, an electrostatic latent image is formed on the surface by an electric potential difference, and the electrostatic latent image is developed by a developer so that a visible image embodied by the developer can be formed on the surface of the photosensitive body.
The visible image is transferred to a printing medium, and the transferred visible image is fused to the printing medium by a fusing unit.
However, a unit body of the light exposing unit and a light exposing unit supporting configuration such as a support frame supporting the light exposing unit, etc., may be deformed by heat generated by the fusing unit.
FIG. 1 is a graph illustrating a position error between an actual exposure position and an intended exposure position and a color registration error V according to an inner temperature of the light exposing unit when light exposing signals corresponding to colors of yellow Y, cyan C, black K and magenta M are exposed upon the corresponding photosensitive bodies. As illustrated in the graph, the color registration error V increases as the temperature increases from the temperature of approximately 35 degrees Celcius, and rapidly increases as the temperature increases to more than 50 degrees Celcius. The illustrated positional errors occur because the light exposing unit designed to expose a uniform light exposure upon a certain position of the surface of the photosensitive body begins to expose light upon other positions different from the intended light exposure position as the temperature increases and the supporting configuration is deformed by the heat.
If the light exposing unit is deformed by heat with respect to the main scanning direction, the light exposure position may be biased in a sub scanning direction (a proceeding direction of the printing medium) which is vertical to the main scanning direction. The bias of the light exposure position in the sub scanning direction has a direction effect on the color registration error.
In the conventional image forming apparatus, to prevent the deformation by heat of the light exposing unit, a separate cooling mode is provided. More particularly, if the temperature of the light exposing unit becomes more than a predetermined value, a printing work is suspended temporarily or the printing speed is reduced according to the cooling mode. However, as the cooling mode is performed, the printing speed decreases.